Anion exchange membranes for redox flow batteries

Abstract

A flow battery having at least one rechargeable cell is disclosed. The at least one rechargeable cell can include an anolyte compartment, a catholyte compartment, and an anion exchange membrane positioned between the anolyte and catholyte compartments. The anion exchange membrane can have a thickness of less than 100 μm and a steady state diffusivity of less than 0.4 ppm/hr/cm 2 with respect to a cation species in an electrolyte of the rechargeable cell. A method of facilitating use of a flow battery including providing the anion exchange membrane is also disclosed. A method of facilitating storage of an electric charge comprising providing the flow battery is also disclosed. A method of producing an anion exchange membrane is also disclosed.

What is claimed is: 
     
       1. A flow battery comprising:
 at least one rechargeable cell including an anolyte compartment configured to hold a first electrolyte having a first cation species; 
 a catholyte compartment configured to hold a second electrolyte having a second cation species; and 
 an anion exchange membrane positioned between the anolyte compartment and the catholyte compartment, configured to be ionically conductive between the first electrolyte and the second electrolyte, the anion exchange membrane formed from a microporous substrate having a thickness of less than 100 μm and a monomer having a cationic functional group and a cross-linking group polymerized to a surface of the microporous substrate, and the anion exchange membrane being fully cross-linked and having a steady state diffusivity of less than 0.4 ppm/hr/cm 2  with respect to at least one of the first cation species and the second cation species. 
 
     
     
       2. The flow battery of  claim 1 , wherein at least one of the first cation species and the second cation species is a metal ion. 
     
     
       3. The flow battery of  claim 2 , wherein at least one of the first cation species and the second cation species is selected from zinc, copper, cerium, and vanadium. 
     
     
       4. The flow battery of  claim 3 , wherein the anion exchange membrane has a useful life of at least about 12 weeks, determined when internal potential drop is at least about 2.5 V. 
     
     
       5. The flow battery of  claim 1 , wherein the anion exchange membrane has a thickness of less than about 55 μm. 
     
     
       6. The flow battery of  claim 5 , wherein the anion exchange membrane has a thickness of between about 15 μm and about 35 μm and the microporous substrate comprises ultrahigh molecular weight polyethylene. 
     
     
       7. The flow battery of  claim 6 , wherein the anion exchange membrane has a thickness of about 25 μm. 
     
     
       8. The flow battery of  claim 7 , wherein the anion exchange membrane has a steady state diffusivity of less than 0.12 ppm/hr/cm 2  with respect to at least one of the first cation species and the second cation species. 
     
     
       9. The flow battery of  claim 1 , wherein the anion exchange membrane has a resistance of between about 3.0 Ω-cm 2  and about 10.0 Ω-cm 2  when measured on direct current after equilibrium in a 0.5M NaCl solution at 25° C. 
     
     
       10. The flow battery of  claim 9 , wherein the anion exchange membrane has a resistance of between about 5.0 Ω-cm 2  and about 8.0 Ω-cm 2  when measured on direct current after equilibrium in a 0.5M NaCl solution at 25° C. 
     
     
       11. The flow battery of  claim 10 , wherein the anion exchange membrane has a co-ion transport number of at least about 0.95 with respect to at least one non-redox species. 
     
     
       12. The flow battery of  claim 1 , configured to be compatible with a high voltage direct current (HVDC) transmission line and provide a voltage of between about 1000V and about 800 KV. 
     
     
       13. The flow battery of  claim 1 , configured to be compatible with an automobile and provide a voltage of between about 100V and about 500V. 
     
     
       14. A method of facilitating use of a flow battery, comprising:
 providing at least one anion exchange membrane formed from a microporous substrate coated with a monomer having a cationic functional group and a cross-linking group polymerized to a surface of the microporous substrate, the anion exchange membrane being fully cross-linked and having a thickness of less than 100 μm and a steady state diffusivity of less than 0.4 ppm/hr/cm 2  with respect to at least one of a first metal cation species and a second metal cation species; and 
 providing instructions to install each anion exchange membrane in a rechargeable cell of the flow battery, between an anolyte compartment and a catholyte compartment. 
 
     
     
       15. The method of  claim 14 , wherein providing the anion exchange membrane comprises providing an anion exchange membrane having a thickness of between about 15 μm and about 35 μm comprising ultrahigh molecular weight polyethylene. 
     
     
       16. The method of  claim 15 , wherein providing the anion exchange membrane comprises providing an anion exchange membrane having a steady state diffusivity of less than 0.12 ppm/hr/cm 2  with respect to at least one of the first metal cation species and the second metal cation species, the first and second metal cation species independently selected from zinc, copper, cerium, and vanadium. 
     
     
       17. The method of  claim 16 , further comprising providing instructions to charge the flow battery and continuously operate the flow battery. 
     
     
       18. A method of facilitating storage of an electric charge, comprising:
 providing a flow battery comprising a plurality of rechargeable cells, each rechargeable cell including:
 an anolyte compartment configured to hold a first electrolyte having a first cation species; 
 a catholyte compartment configured to hold a second electrolyte having a second cation species; and 
 an anion exchange membrane positioned between the anolyte compartment and the catholyte compartment, configured to be ionically conductive between the first electrolyte and the second electrolyte, the anion exchange membrane formed from a microporous substrate coated with a monomer having a cationic functional group and a cross-linking group polymerized to a surface of the microporous substrate, the anion exchange membrane being fully cross-linked and having a thickness of less than 100 μm and a steady state diffusivity of less than 0.4 ppm/hr/cm 2  with respect to at least one of the first cation species and the second cation species; and 
 
 providing instructions to charge the flow battery. 
 
     
     
       19. The method of  claim 18 , further comprising providing instructions to charge the flow battery by electrically connecting the flow battery to a variable energy supply. 
     
     
       20. The method of  claim 18 , further comprising providing instructions to electrically connect the flow battery to a high voltage direct current (HVDC) transmission line. 
     
     
       21. The method of  claim 20 , further comprising providing instructions to replace at least one of the first electrolyte and the second electrolyte after discharge of the flow battery. 
     
     
       22. A flow battery comprising:
 at least one rechargeable cell including 
 an anolyte compartment configured to hold a first electrolyte having a first cation species; 
 a catholyte compartment configured to hold a second electrolyte having a second cation species; and 
 an anion exchange membrane positioned between the anolyte compartment and the catholyte compartment, configured to be ionically conductive between the first electrolyte and the second electrolyte, the anion exchange membrane formed from a microporous substrate having a thickness of less than 100 μm and a monomer having a cationic functional group and a cross-linking group polymerized to a surface of the microporous substrate and cross-linked without a cross-linking agent, and the anion exchange membrane having a steady state diffusivity of less than 0.4 ppm/hr/cm 2  with respect to at least one of the first cation species and the second cation species. 
 
     
     
       23. The flow battery of  claim 22 , wherein the anion exchange membrane is fully cross-linked.